One method to control intake and exhaust valve operation during engine operation is described in U.S. Pat. No. 6,332,446. This method uses electromechanically actuated valves to control vibration of an internal combustion engine caused by cylinder deactivation. The method causes at least one of a plurality of cylinders to operate in a cylinder deactivation mode in which the intake stroke, combustion stroke and exhaust stroke are inhibited. The method then controls the pressure within each inactive cylinder that operates in the cylinder deactivation mode.
Once the above-mentioned method has set the stroke of each cylinder, timing of valve opening and closing is determined by retrieving a map based on accelerator pedal position and engine speed. Finally, a further valve timing adjustment is made to correct for air-fuel errors and valve operating conditions. Specifically, valve temperature and power supply voltage are referenced to correct valve opening and closing times.
The inventors herein have determined that the before-mentioned approach can have several disadvantages. Specifically, while it may adjust electromechanical valve opening and closing time based on supply voltage, variations in the electrical system can still lead to degraded performance. For example, if the vehicle experiences temporary reduced power conditions, there may be insufficient electrical energy to operate all of the valves as suggested in the prior art. Further, the vehicle battery may not have enough stored energy to crank the engine. Further still, even if there is sufficient electrical energy, the overall efficiency of the system can become degraded if too many electrically actuated valves are operated.